A polarizing plate has been applied to various display devices such as a liquid crystal display device, an organic electroluminescent device, etc. A polarizing plate which is manufactured by laminating a protective film on one surface or both surfaces of a polyvinyl alcohol (hereinafter, referred to as “PVA”)-based polarizer manufactured by dyeing a PVA-based film with an iodine and/or dichroic dye, crosslinking the iodine and/or dichroic dye with boric acid, and aligning the film by stretching is currently mainly used.
Meanwhile, recently, applications of display devices have been widely expanded to portable devices and household large-sized TVs, and technologies for providing excellent display quality of each display device have been developed accordingly. Uniform transmittance and color of a polarizer as well as the degree of polarization are important for display quality of a display device.
Conventionally, a method of adjusting a time or temperature of immersing a PVA-based film in a processing bath has been used to adjust transmittance and color of a PVA-based polarizer. However, the method of adjusting a time and a temperature in a processing bath has a problem that if stretching conditions are modified in a stretching step, time and temperature conditions in the processing bath need to be adjusted.
Meanwhile, recently, display devices have been required to continuously increase the transmittance of a polarizing plate for the sake of energy efficiency. However, in general, if the transmittance of a polarizing plate used in a liquid crystal display device and an organic light emitting diode is increased, a light absorption area of a complex of a PVA-based film and a dichroic dye is decreased, so that the absorbance and the cross transmittance in a short wavelength or long wavelength region are considerably decreased.
Accordingly, the polarizing plate may have deterioration in polarizing performance and thermal durability and hardly maintain a neutral color, as compared with a polarizing plate with a low transmittance.